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71.
Bergquist Peter L. Te’o V. S. Junior Gibbs Moreland D. Cziferszky Angela C. E. De Faria Fabricia P. Azevedo Maristela O. Nevalainen K. M. Helena 《Applied biochemistry and biotechnology》2002,98(1-9):165-176
Cost-effective production of enzymes for industrial processes makes the appropriate selection of the host-vector expression
system critical. We have developed two systems for the bulk production of bleaching enzymes from thermophiles. Kluyveromyces lactis has been developed as a secretion host employing expression vectors based on the 2μ-like plasmid pKD1 of Kluyveromyces drosophilarium. Our second system involves the filamentous fungus Trichoderma reesei. Fusion and nonfusion vectors have been constructed using the strong cellobiohydrolase 1 (cbh1) promoter. The KEX2 protease cleavage site and a 6 × HIS-tag have been incorporated to facilitate both cleavage and purification
of the mature foreign proteins. 相似文献
72.
Catellani M Mealli C Motti E Paoli P Perez-Carreño E Pregosin PS 《Journal of the American Chemical Society》2002,124(16):4336-4346
A series of dichloro-bridged arylbicycloheptylpalladium complexes have been synthesized and characterized by means of NMR spectroscopy. The compound [(C16H19)PdCl]2*CH2Cl2 with ortho and para methyl substituents at the arene has been characterized by means of X-ray diffraction techniques. The C(ipso) atom of the arene lies almost at the fourth planar coordination site of the metal [Pd-C(ipso) = 2.22(1) A (average)], and due to the arene's tilting, the substituted C(ortho) atom is relatively close to the metal atom [2.54(1) A (average)]. The coordinated C(ipso)-C(ortho) linkage, in a seemingly dihapto coordination, is anti with respect to the CH2 bridge of the bicycloheptyl unit. Variable-temperature NMR experiments for the para-substituted dimer 9 reveal restricted rotation of the two aryl groups about the corresponding C-C(ipso) bonds (DeltaE < or =17 kcal x mol(-1)). DFT-B3LYP calculations have been carried out on the known and similar monomer (phenylbicycloheptenyl)Pd(PPh3)I (4) and its related substituted derivatives. The essential results are as follows: (i) The potential energy surface for twisting the phenyl ring away from the symmetric eta(1) coordination in 4 is very flat (DeltaE < or = 1 kcal x mol(-1)) whereas an Atoms in Molecules analysis excludes the existence of an actual Pd-C(ortho) bond in the seemingly eta2-type conformer. (ii) Complete rotation of the unsubstituted phenyl ring is not facile but feasible. A significant strain affects the transition-state structure featuring a Pd-HC(aryl) agostic-type bond. The calculated destabilization of 10.3 kcal x mol(-1), with respect to the ground state, can be compared to the experimental barrier of the dimer 9. (iii) Various methyl-substituted derivatives of 4 have been optimized, and their structural and energetic trends are discussed. An almost ideal eta1 coordination is shown by the anti conformer of the C(ortho)-substituted complex due steric effects. For all of the other cases, a slipped eta2 coordination may be described. As a general conclusion, the unsaturated metal center receives pi electron density of the arene mainly through its C(ipso) atom. The effect may be slightly improved if the C(ortho) atom also gets closer to the metal, but in no case, does the slipped eta2 coordination seem to be crucial for the stability of the system. 相似文献
73.
Barros N. Feijóo S. Simoni A. Critter S. A. M. Airoldi C. 《Journal of Thermal Analysis and Calorimetry》2000,63(2):577-588
The microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms,
ΔH
met. This parameter has been calculated by microcalorimetry for many organic, inorganic and biochemical reactions, but there
is only some information about its quantification for microbial growth reactions in soils. Values of ΔH
met were calculated for different soil samples collected in Galicia (Spain) and Campinas (Săo Paolo, Brazil). Exponential microbial
growth was stimulated in all soil samples by the addition of glucose and power-time curves were recorded. Results showed changes
in the values of ΔH
met calculated for all the soil samples, suggesting a dependence of this value with the microbial growth rate constant, with
the percentage of growth, with the initial number of microorganisms of soil samples, with the quantity of glucose added and
with the strain of bacteria growing in soil.
The interpretation of variations of ΔH
met provides important qualitative and quantitative information. It reports data that allow to interpret from a qualitative point
of view, the increase in biomass as a consequence of the degradation of the organic matter in soil, to understand changes
in the percentages of soil organic matter and to know if the microbial population growing in differential soil samples is
homogeneous. Therefore, to report that value would be very important in ecological studies, but beforehand, it is necessary
to solve some problems that can appear in the experiments done to make the quantification
.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
74.
An amperometric flow-injection method for the determination of antithyroid drugs such as 6-methyl-2-thiouracil (MTU) using a carbon fiber cylindrical microelectrode-based detector is reported. A home-made flow-cell specially adapted for working with cylindrical microelectrodes ranging between 4 and 10 mm in length was used for this purpose. Methanol containing 0.05 mol l(-1) tetrabutylammonium perchlorate as the supporting electrolyte was employed, and a potential of +1.6 V was selected for the amperometric detection of MTU. No cleaning or electrode surface regeneration of the fiber was necessary during the whole working day. A limit of detection of 2.6x10(-7) mol l(-1) (37 mug MTU l(-1)) was achieved. The method was applied to the determination of MTU in spiked feed samples (peas and corn flour), at the 142 mug g(-1) level. The procedure involved the extraction of the drug in methanol, a clean-up step using Florisil cartridges and the use of the standard additions method. Recoveries of 81+/-6 and 85+/-8% were obtained for peas and corn flour, respectively. 相似文献
75.
López-Alarcón C Squella JA Núñez-Vergara LJ Baez H Camargo C 《Rapid communications in mass spectrometry : RCM》2002,16(24):2229-2238
A gas chromatography/mass spectrometry (GC/MS) method for the qualitative and quantitative determination of the calcium-channel antagonists C-4-substituted 1,4-dihydropyridines, and their corresponding N-ethyl derivatives, is presented. Also, the electrochemical oxidation and the reactivity of the compounds with alkyl radicals derived from 2,2'-azobis-(2-amidinopropane) were monitored by GC/MS. Mass spectral fragmentation patterns for the C-4-substituted 1,4-dihydropy-ridine parent drugs were significantly different from those of their oxidation products, generated either by electrochemical oxidation or by reaction with alkyl radicals. However, for N-ethyl-1,4-dihydropyridine compounds it was not possible to detect the final products (pyridinium salts) using these experimental conditions. 相似文献
76.
M. Kabešová I. Vargová T. Šramko J. Gažo 《Journal of Thermal Analysis and Calorimetry》1978,13(1):65-70
The influence of the position of the CH3 group in picoline and lutidine ligands on the degree of chemical change of the NCS groups in coordination compounds of the type Cu(NCS)2L2 (whereL=2-, 3- and 4-picoline, and 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-lutidine) is dealt with. The most marked effect of the CH3 group is found to be exerted in position 4. This effect of the methyl group on the degree of chemical change points to the mutual influence of the ligands in coordination compounds of Cu(II).
Zusammenfassung Der Artikel befaßt sich mit dem Einfluß der Lage der CH3 Gruppe in Pikolinen und Lutidinen als Liganden auf den Grad der chemischen Änderungen der Gruppen NSC in Koordinationsverbindungen des Typs Cu(NCS)2L2 (L=2-, 3- und 4-Pikoline, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- und 3,5-Lutidine). Der ausgeprägteste Effekt der CH3 Gruppe wurde in der Position 4 beobachtet. Dieser Einfluß der Methylgruppe auf das Ausmaß der chemischen Änderungen deutet auch auf die gegenseitige Wirkung der Liganden in Koordinationsverbindungen von Cu(II).
Résumé L'article a trait à l'influence de la position du groupe CH2 dans les picolines et lutidines, en tant que ligands, sur le degré des changements chimiques des groupes SCN dans les composés de coordination du type Cu(SCN)2L2 (L=2-, 3 et 4-picoline, 2,3-, 2,4-,2,5-, 2,6-, 3,4- et 3,6-lutidine). L'effet le plus prononcé du groupe CH3 s'observe en position 4. Cette influence du groupe méthyle sur le degré des changements chimiques indique aussi l'influence mutuelle des ligands dans les composés de coordination du Cu(II).
- , , NCS Cu(NCS)2,L2, L=2-, 3- 4- , 2.3-, 2.4-, 2.5-, 2.6-, 3.4- 3.5-. , 4. Cu(II).相似文献
77.
Chaboy J Muñoz-Páez Díaz-Moreno S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(5):1102-1108
An extensive study on the appearance of multi-electron features in the X-ray absorption spectra of several yttrium(III)-based compounds has been performed. The existence of a multi-electron transition of non-negligible intensity within the extended X-ray absorption fine structure (EXAFS) region of the Y K-edge spectra has been proven. The impact of such features in the EXAFS analysis is made evident for aqueous solutions of YBr3 x 6H2O in liquid and glassy states in the concentration range 0.005-2.0 M, in which this transition induces an overestimation in the coordination numbers derived from EXAFS. We have performed theoretical computation of cross-sections for the double-electron processes at the K-edge of both Y and Br. These computations have been applied to the experimental EXAFS K-edge spectra of both Y and Br in several solids and in aqueous solutions. While in the case of Y K-edge spectra the presence of such multi-electron transitions was seen to seriously affect the standard EXAFS analysis, its influence in the case of Br K-edge spectra was determined to be negligible. 相似文献
78.
We calculate energy barriers of atom- and proton-transfer reactions in hydrogen-bonded complexes in the gas phase. Our calculations do not involve adjustable parameters and are based on bond-dissociation energies, ionization potentials, electron affinities, bond lengths, and vibration frequencies of the reactive bonds. The calculated barriers are in agreement with experimental data and high-level ab initio calculations. We relate the height of the barrier with the molecular properties of the reactants and complexes. The structure of complexes with strong hydrogen bonds approaches that of the transition state, and substantially reduces the barrier height. We calculate the hydrogen-abstraction rates in H-bonded systems using the transition-state theory with the semiclassical correction for tunneling, and show that they are in excellent agreement with the experimental data. H-bonding leads to an increase in tunneling corrections at room temperature. 相似文献
79.
Berezkin Victor G. Mardanov Robert G. Moiseew Aleksey A. Malinowska Irena Różyło Jan K. 《平面色谱法杂志一现代薄层色谱法》2002,15(5):377-379
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
80.
Concha-Graña E Turnes-Carou MI Muniategui-Lorenzo S López-Mahía P Fernández-Fernández E Prada-Rodríguez D 《Journal of chromatography. A》2004,1047(1):147-155
The scope of this work is the development of a rapid, reliable and sensitive method for the analysis of organochlorine pesticides from soils by pressurized liquid extraction (PLE). The effect of four parameters (temperature, pressure, static time and cell volume) on the extraction efficiency was studied. The great extracting power of the PLE causes the extraction of numerous interfering substances, so a more efficient purification of this extract was necessary. In this work several sorbents have also been assayed to carry out the purification of soil samples: Florisil, silica, alumina, carbon, as well as combinations of them. Finally, the proposed analytical method was validated using a certified reference soil material (CRM804-050) and the results were compared with those obtained by other extraction techniques (Soxhlet and microwave-assisted extraction). 相似文献